In the art of liquid scintillation counting of a flowing sample, particularly where a sample material is subjected to liquid chromatography prior to analysis in a liquid scintillation counter, the liquid scintillation instrument generally utilizes an apparatus through which a sample solution including scintillation cocktail is flowed in proximity to a light detector. Such an apparatus through which the sample is flowed is generally referred to as a flow cell. Each of the separated bands in the sample solution emit a characteristic light emission due to the scintillation cocktail, which passes through a transparent portion of the flow cell to the photodetector to be detected. The information obtained from a detected light provides analysis of the sample.
Typically, a flow cell comprises a length of transparent tubing which is permanently arranged in a coil-like fashion such that light emissions from the sample solution flowing therethrough are concentrated to be received and detected by the photodetector. The tubing is selected having a small diameter to maintain sample resolution with a select length to provide a fixed volume of sample solution contained therein having exposure of the photodetector. The chosen length of tubing determines the volume of fluid contained within the flow cell exposed to the photodetector.
While the diameter of the transparent tubing is generally maintained consistent, varying lengths of tubing are utilized to provide differing volumes of sample solution for exposure to the photodetector. A greater volume of sample solution generally provides greater sensitivity in the detection of light, i.e. radioactivity in the sample solution by the scintillation instrument. Thus, in a constant flow system use of a longer length of tubing permits a given volume of fluid to be exposed to the photodetector for a longer period of time as it flows through the tubing permitting a longer term of measurement. This longer exposure period improves sensitivity. However a longer length of tubing providing a greater volume in the tubing coil of the flow cell has a disadvantage in that the separated bands of the sample solution which has been processed through liquid chromatography begin to diffuse and remix degrading resolution and accuracy of the analysis. Thus, depending on the sample material and the quality of separation in the sample solution, a large volume flow cell can be a disadvantage even though it may provide greater sensitivity.
Depending on the experiment to be performed an experimentor must select a flow cell having a volume which they believe is appropriate for the particular experiment, weighing the need of sensitivity in the detection of light versus the need of resolution in the chromatography for sample analysis. This selection may be different for each experiment and for each experimentor. Thus, a number of different fixed volume flow cells are generally made available to an experimentor for his selection and use. Such flow cells are for example manufactured and sold by Berthold Company of Wildbad, West Germany under Part Numbers Z-2000 and Z-4000.
The use of a number of different fixed volume flow cells however requires an experimentor to stock many different types in order to have them available so that they may have the freedom to select that specific volume flow cell which they deem appropriate for a given experiment. This can be expensive and often is troublesome in that it requires inventory space to maintain such a collection which could be used otherwise.